Advanced switch node selection for power line communications network

ABSTRACT

An algorithm for the promotion of terminal nodes to switch nodes in a PLC network reduces overall network overhead and collisions, while ensuring the appropriate selection of a switch node and minimizing the number of levels in a PLC network. It also ensures that the terminal nodes with appropriate signal-to-noise ratios (SNRs) are promoted. It is desirable to have a network with fewer levels. The disclosed approach favors the nodes that are closer to the DC to promote them as switch nodes. This is achieved by waiting for a smaller number of PNPDUs for a node that is closer to the DC in comparison to a node that is farther away from the DC.

FIELD

The present invention relates generally to power line communicationnetworks, and more specifically to promoting a terminal node to a switchnode.

BACKGROUND

Power line communication or power line carrier (PLC) is a system forcarrying data on a conductor also used for electric power transmission.A wide range of power line communication technologies are needed fordifferent applications, ranging from home automation to Internet access.

Electrical power is transmitted over long distances using high voltagetransmission lines, distributed over medium voltages, and used insidebuildings at lower voltages. Hence, electrical power grids allow forrelatively low cost communication over long distances. Full- andhalf-duplex systems (both one-way and two-way systems) have beensuccessfully used for decades for purposes such as automatic remotemeter readings.

Power line communications systems operate by impressing a modulatedcarrier signal on a wiring system. Different types of power linecommunications use different frequency bands, depending on the signaltransmission characteristics of the power wiring used. Since the powerdistribution system was originally intended for transmission of AC powerat typical frequencies of 50 Hz or 60 Hz, power wire circuits have onlya limited ability to carry higher frequencies. The propagation problemis a limiting factor for each type of power line communications. Datarates and distance limits vary widely over many power line communicationstandards. Low frequency (about 100-200 kHz) carriers impressed onhigh-voltage transmission lines may carry one or two analog voicecircuits, or telemetry and control circuits with an equivalent data rateof a few hundred bits per second; however, these circuits may be manymiles long. Higher data rates generally imply shorter ranges; a localarea network operating at millions of bits per second may only cover onefloor of an office building, but eliminates the need for installation ofdedicated network cabling.

Narrowband power line communications began soon after electrical powersupply became widespread. Around the year 1922 the first carrierfrequency systems began to operate over high-tension lines withfrequencies of 15 to 500 kHz for telemetry purposes, and this continues.Consumer products such as baby alarms have been available at least since1940. In the 1930's, ripple carrier signaling was introduced on themedium (10-20 kV) and low voltage (240/415 V) distribution systems. Formany years, the search continued for a low cost bi-directionaltechnology suitable for applications such as remote meter reading. TheEDF (French power utility) prototyped and standardized a system called“spread frequency shift keying” or S-FSK. (See IEC 61334.) This systemis now a simple, low-cost system with a long history. However, it has avery slow transmission rate, between 200 and 800 bits per second. In the1970's, the Tokyo Electric Power Co. ran experiments that reportedsuccessful bi-directional operation with several hundred units. Sincethe mid-1980's, there has been a surge of interest in using thepotential of digital communications techniques and digital signalprocessing. The drive is to produce a reliable system that is cheapenough to be widely installed and able to compete cost effectively withwireless solutions.

Applications of mains communications vary enormously, as would beexpected of such a widely available medium. One natural application ofnarrow band power line communication is the control and telemetry ofelectrical equipment such as meters, switches, heaters and domesticappliances. A number of active developments are considering suchapplications from a systems point of view, such as demand sidemanagement wherein domestic appliances would intelligently co-ordinatetheir use of resources, for example limiting peak loads. Control andtelemetry applications include both ‘utility side’ applications, whichinvolve equipment belonging to the utility company up to the domesticmeter, and ‘consumer-side’ applications that involve equipment in theconsumer's premises. Possible utility-side applications includeautomatic meter reading (AMR), dynamic tariff control, load management,load profile recording, credit control, pre-payment, remote connection,fraud detection and network management, and could be extended to includegas and water. A project of EDF, France includes demand management,street lighting control, remote metering and billing, customer specifictariff optimization, contract management, expense estimation and gasapplications safety. Many specialized niche applications also exist thatuse the mains supply within the home as a convenient data link fortelemetry. For example, in the UK and Europe a TV audience monitoringsystem uses power line communications as a convenient data path betweendevices that monitor TV viewing activity in different rooms in a homeand a data concentrator that is connected to a telephone modem.

Several competing organizations have developed specifications, includingthe HomePlug Powerline Alliance, Universal Power line Association andHD-PLC Alliance. On December 2008, the ITU-T adopted recommendationG.hn/G.9960 as a standard for high-speed power line, coax and phone linecommunications. The National Energy Marketers Association was alsoinvolved in advocating for standards. IEEE P1901 is an IEEE workinggroup developing the global standard for high-speed power linecommunications. In July 2009, the working group approved its “IEEE 1901Draft Standard for Broadband over Power Line Networks: Medium AccessControl and Physical Layer Specifications” as an IEEE draft standard forbroadband over power lines defining medium access control and physicallayer specifications. The IEEE 1901 Draft Standard was published by theIEEE in January 2010, and the final standard was approved on 30 Sep.2010 and published on Feb. 1, 2011. NIST has included IEEE 1901,HomePlug AV and ITU-T G.hn as “Additional Standards Identified by NISTSubject to Further Review” for the smart grid in the United States.PRIME is one of the narrowband PLC technologies that has been widelyadopted in Spain by utilities such as Iberdrola and Union Fenosa.Specifically, PRIME PLC system operation is defined in the draftSpecification for Power Line Intelligent Metering Evolution incorporatedby reference herein.

Increased use of PLC systems has generated the need for regularlyobtaining data from all metered points in order to better control andoperate the system. Specifically, there is a need for efficientselection of a switch node at the data concentrators, while alsoensuring that the best possible node is chosen to be promoted as aswitch node.

SUMMARY

Embodiments disclosed herein address the above stated needs by providingan efficient algorithm for optimal switch node selection in PLC systems.

According to one method embodiment, a switch node in a Power LineCommunication (PLC) network is selected by initiating, by a new terminalnode, a request to join the PLC network, sending, by neighboringterminal nodes to a base node, requests to be promoted to a switch node,and selecting a new optimal switch node by the base node. The selectionof the new switch node is determined by a probabilistic algorithmaccording to a generated random number, and by transmitting a promotionmessage by the base node to the selected terminal node, which thenbecomes a new switch node for the new terminal node. The new switch nodetransmits beacons requesting the new node to join the network.

According to a system embodiment, a system includes a switch node to beselected in a Power Line Communication (PLC) network. The systemincludes a new terminal node requesting to join the PLC network and abase node having a data concentrator for selection of a new optimalswitch node. The selection of the new switch node is determined by aprobabilistic algorithm according to a generated random number, and bytransmitting a promotion message to the new optical switch node.Neighboring terminal nodes send requests to the base node to be promotedto a switch node and transmitting beacons requesting the new node tojoin the network.

According to algorithm embodiment, an optimum switch node in a PowerLine Communication (PLC) network is selected. The algorithm operates toreceive requests at a base node having a data concentrator from terminalnodes asking to be promoted to a switch node to serve a new node tryingto join the network. The algorithm verifies, by a terminal node, thatthere is an acceptable Signal to Noise Ratio (SNR) of a receivedPromotion Needed Protocol Data Unit (PNPDU) request. The algorithmgenerates a random number back-off for the purpose of reducing networkcongestion and transmits, by a terminal node, a Promotion Up processmessage to the base node based on a probabilistic function according toa delay based on the level of the node and the generated random numbermultiplied by a level of node PNPDUs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a power linecommunication network in which advanced switch node selection can beused;

FIG. 2 is an exemplary overview flowchart illustrating advanced switchnode selection;

FIG. 3 is a detailed flowchart illustrating an exemplary promotion uptransmission procedure during advanced switch node selection; and

FIG. 4 is a state diagram illustrating an exemplary promotion downselection procedure during advanced switch node selection.

In the various figures of the drawing, like reference numbers are usedto denote like or similar parts.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

An algorithm for reducing overall network overhead while ensuring theappropriate selection of a switch node and minimizing the number oflevels in a PLC network is disclosed. The algorithm ensures that trafficoverhead is mitigated during the node promotion process. It also ensuresthat the terminal nodes with appropriate Signal-to-noise ratios (SNRs)are promoted. The algorithm describes the promotion procedure for aterminal node to a switch node.

FIG. 1 is a diagram illustrating an example of a power linecommunication network 100 in which advanced switch node selection can beused. Electrical power is transmitted from a generating station 102 to astep-up transformer 104 where voltage is increased for transmission overlong distances using high voltage transmission lines 106 b. Voltages maybe increased at the step-up transformer 104 or one or more transmissionsubstations 108 to values between 765 kV-230 kV 138 kV before reaching adistribution substation 110. At the distribution substations 110,voltages may be stepped down using a substation step-down transformer112 for delivery to customers over distribution transmission lines 106b. For example, 26 kV and 69 kV power may be distributed to asub-transmission customer 114 such as a large factory. 13 kV power maybe distributed to a primary customer such as medium-sized factories. 120V and 240 V power may be distributed to secondary, or residential,customers. Distribution substations 110 are typically base nodescontaining a data concentrator (not shown). Thus, FIG. 1 illustrates anexemplary grid network from the generating station to the consumer thatcan be used for powerline communication.

FIG. 2 is an exemplary overview flowchart illustrating advanced switchnode selection 200. The advanced switch node algorithm may be detailedin terms of the draft Specification for Power Line Intelligent MeteringEvolution. However, one skilled in the art would recognize that theadvanced switch node algorithm is applicable to any PLC standard.

When a new terminal node attempts to join the network, it initiates arequest message in step 202. For example, in the PRIME standard, a PNPDU(Promotion Needed Protocol Data Unit) request is issued in a data frameif the terminal node cannot detect any beacon from an existing switchnode. This data frame essentially requests for a data concentrator orbase node (BN), typically located at a distribution substation 110, topromote one of the terminal nodes in the neighborhood of the newterminal node into a switch node.

The PNPDU is a one-hop broadcast, which can potentially be heard bymultiple terminal nodes in the neighborhood. In step 204, theneighboring terminal nodes send PROMOTION UP PROCESS (PRO_REQ_S) framesto the BN requesting for that node to be promoted to a switch node toserve the new node trying to join the network in step 204. Control flowproceeds to step 206.

In step 206, the data concentrator, or base node, will determine theappropriate terminal node that needs to be promoted into a switch nodebased on a proprietary algorithm comprising promotion up and demotiondown procedures detailed in FIGS. 3 and 4 respectively. Control flowproceeds to step 208.

In step 208, the data concentrator transmits a PRO_DN (PRO_REQ_B)message to the terminal node to be promoted as a switch node. Controlflow proceeds to step 210.

In step 210, the newly promoted switch node transmits beacons for thenew terminal node to join the network. In this fashion, the new node canjoin the network even if it is not able to hear any beacons initially.

FIG. 3 is a detailed flowchart illustrating an exemplary Promotion UpTransmission procedure during advanced switch node selection 206. ThePromotion Up Transmission procedure reduces the overall levels in thenetwork as well as the number of switches, while ensuring that theswitches are sufficiently robust, having a SNR greater than apredetermined threshold) when communicating with the new node. It alsoensures that the traffic overhead during the procedure is mitigated andthat the network is stable during the node promotion process.

The promotion up transmission starts in step 302 after the base nodereceives requests from terminal nodes asking to be promoted to a switchnode in order to serve the new node trying to join the network. Controlproceeds to step 304.

In step 304, when a terminal node receives a PNPDU, it adds it to aPNPDU list along with the PNA, or extended unique identifier (EUI)address. Control flow proceeds to step 306.

In step 306, if the terminal node is already engaged in a promotion upprocess for this requesting terminal node or any other requestingterminal node, there is no need to initiate a Promotion Up process andcontrol flow proceeds accordingly to step 308 where no promotion isneeded and control flow proceeds to step 310. Otherwise, control flowproceeds to step 322.

In step 322, the terminal node first verifies the SNR of the receivedPNPDU. If the SNR is below a predetermined threshold (e.g. 10 dB), apromotion up procedure is not performed for this node and control flowproceeds to step 308 where no promotion is needed and control flowproceeds to step 310. Otherwise, the SNR is acceptable for effectivecommunication with the new node and control flow proceeds to step 316.

In step 316, the terminal node first generates a random number forbackoff purposes in reducing network congestion. Control flow proceedsto step 314.

In step 314, the terminal node transmits a promotion up process messageto the base node based on a probabilistic function according to therandom number generated in step 316 and control flow proceeds to step310. The promotion up request is transmitted according to a delay basedon the level of the node after receiving a random number multiplied bythe level of node PNPDUs. It is desirable to have a network with fewerlevels, and this approach favors the nodes that are closer to the DC topromote them as switch nodes. This is achieved by waiting for a smallernumber of PNPDUs for a node that is closer to the DC in comparison to anode that is farther away from the DC.

The promotion up request is generated only after this delay and will betransmitted as per the CSMA/CA procedure in PRIME. Since PNPDUs aregenerated at a fairly high rate by each node in PRIME, it should benoted that the promotion up process frames do not require anyretransmission unlike other control frames because PNPDU generation willautomatically trigger multiple transmissions of PRO_REQ_S frames by thesame node.

In step 310, the PNPDU list is checked for more unique EUI addresses. Ifthere are no more unique addresses in the list, control flow ends instep 312. Otherwise control flow proceeds to step 318.

In step 318, if a predetermined timeout period has expired, the node canaccept any PNPDUs from the same requesting node or any other node toperform the promotion up procedure and control returns to step 304.Otherwise, control flow proceeds to step 320, where the node is waitingfor a response from the DC (PRO_REQ_B frame) for any ongoing promotionprocess, before then returning to step 304.

FIG. 4 is a state diagram illustrating an exemplary promotion downselection procedure 400, or demotion process, of advanced switch nodeselection. The base node 402 or a switch node (404, 408, 410) maydiscontinue the switching function of a new node 406 at any time. Thedemotion mechanism provides this process using a PRO control packet forall demotion transactions. The PRO.NSID field of the PRO control packetcontains the SID of the node that is being demoted as part of thedemotion transaction. The PRO.PNA field is not used in any demotionprocess transaction and its contents are not interpreted at either end.Following the successful completion of a demotion process, a switch nodeshall immediately stop the transmission of beacons and change from aswitch functional state to a terminal functional state. The base nodemay reallocate the SID and beacon slot used by the demoted switch after(macMaxCtlReTx+1)*macCtlReTxTimer seconds to other terminal nodesrequesting promotion.

In this manner, an efficient algorithm for promoting switch node, whilealso ensuring that the best possible node is chosen to be promoted as aswitch node is disclosed. All terminal nodes that hear a request messageto start the promotion process at the same time are prevented fromflooding in the network disrupting the transmission of control (ALVmessages) and data (short cycle and long cycle meter read) traffic tothe nodes that are already part of the network. Because the promotionrequests are spaced out from different nodes within a neighborhood, theprocedure allows for lesser traffic and maintains the connectivity inthe network and availability for meter reading and other operations.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such asinfrared, radio, and microwave, then the coaxial cable, fiber opticcable, twisted pair, DSL, or wireless technologies such as infrared,radio, and microwave are included in the definition of medium. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and blu-ray disc wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Electrical connections, couplings, and connections have been describedwith respect to various devices or elements. The connections andcouplings may be direct or indirect. A connection between a first andsecond electrical device may be a direct electrical connection or may bean indirect electrical connection. An indirect electrical connection mayinclude interposed elements that may process the signals from the firstelectrical device to the second electrical device.

Although the invention has been described and illustrated with a certaindegree of particularity, it should be understood that the presentdisclosure has been made by way of example only, and that numerouschanges in the combination and arrangement of parts may be resorted towithout departing from the spirit and scope of the invention, ashereinafter claimed.

1. A method of selecting a switch node in a Power Line Communication(PLC) network comprising: initiating, by a new terminal node, a requestto join the PLC network; sending, by neighboring terminal nodes to abase node, requests to be promoted to a switch node; selection of a newoptimal switch node by the base node, wherein the selection of the newswitch node is determined by a probabilistic algorithm according to agenerated random number; transmitting a promotion message by the basenode to the selected terminal node, wherein the selected terminal nodebecomes a new switch node for the new terminal node; and transmitting,by the new switch node, beacons requesting the new node to join thenetwork.
 2. The method of claim 1 wherein the probabilistic algorithmfavors nodes for selection that are closest to a data concentrator. 3.The method of claim 1 wherein the probabilistic algorithm waits for asmaller number of promotion requests for a node that is closer to a dataconcentrator in comparison to a node that is farther away from theconcentrator, producing fewer network levels.
 4. The method of claim 1wherein the new terminal requests to join the network are PromotionNeeded Protocol Data Unit (PNPDU) requests.
 5. The method of claim 1wherein requests from neighboring terminal nodes are PROMOTION UPPROCESS (PRO_REQ_S) frames to the base node requesting for those nodesto be promoted to a switch node to serve the new node trying to join thenetwork.
 6. The method of claim 1 wherein the promotion messagetransmitted to the selected terminal node is a PRO_DN (PRO_REQ_B)message.
 7. The method of claim 1 wherein the new terminal joins anetwork without initially hearing any beacons.
 8. A system for selectinga switch node in a power line communication (PLC) network comprising: anew terminal node requesting to join the PLC network; a base node havinga data concentrator for selection of a new optimal switch node, whereinthe selection of the new switch node is determined by a probabilisticalgorithm according to a generated random number, and transmitting apromotion message to the new optical switch node; and neighboringterminal nodes for sending requests to the base node to be promoted to aswitch node and transmitting beacons requesting the new node to join thenetwork.
 9. The system of claim 8 wherein the probabilistic algorithmfavors nodes for selection that are closest to a data concentrator. 10.The system of claim 8 wherein the probabilistic algorithm waits for asmaller number of promotion requests for a node that is closer to a dataconcentrator in comparison to a node that is farther away from theconcentrator, producing fewer network levels.
 11. The system of claim 8wherein the new terminal requests to join the network are PromotionNeeded Protocol Data Unit (PNPDU) requests.
 12. The system of claim 8,wherein requests from neighboring terminal nodes are PROMOTION UPPROCESS (PRO_REQ_S) frames to the base node requesting for those nodesto be promoted to a switch node to serve the new node trying to join thenetwork.
 13. The system of claim 8 wherein the promotion messagetransmitted to the selected terminal node is a PRO_DN (PRO_REQ_B)message.
 14. The system of claim 8 wherein the new terminal joins anetwork without initially hearing any beacons:
 15. An algorithm forselecting an optimum switch node in a Power Line Communication (PLC)network comprising: receiving requests at a base node having a dataconcentrator from terminal nodes asking to be promoted to a switch nodein order to serve a new node trying to join the network; verifying, by aterminal node, that there is an acceptable Signal to Noise Ratio (SNR)of a received Promotion Needed Protocol Data Unit (PNPDU) request;generating a random number backoff purposes in reducing networkcongestion; and transmitting, by a terminal node, a Promotion Up processmessage to the base node based on a probabilistic function according toa delay based on the level of the node and the generated random numbermultiplied by a level of node PNPDUs.
 16. The algorithm of claim 15wherein fewer level are created by favoring the nodes that are closer tothe data concentrator to promote them as switch nodes.
 17. The algorithmof claim 15 wherein the algorithm waits for a smaller number ofpromotion requests for a node that is closer to a data concentrator incomparison to a node that is farther away from the concentrator,producing fewer network levels.
 18. The algorithm of claim 15 wherein ifthe terminal node is already engaged in a Promotion Up process for thisrequesting terminal node or any other requesting terminal node, there isno need to initiate a Promotion Up process.
 19. The algorithm of claim15 wherein if the SNR is below a predetermined threshold, a Promotion Upprocess is not performed for this node.
 20. The algorithm of claim 15wherein when a terminal node receives a PNPDU, it adds it to a PNPDUlist along with an Extended Unique Identifier (EUI) address.